I love watching preschoolers undergo non-traumatic tests that depend on some sort of voluntary response from them. When Jacob was two, we had to get his vision tested. He was supposed to identify various black and white pictures. As soon as he saw the birthday cake, he was so excited that he yelled "BIRTHDAY CAKE" no matter what they showed him. At Bryan's four-year-old checkup he had a hearing test. The nurse asked him to say, "Beep," whenever he heard a beeping sound. It went down something like this...
Stage 1: (30 seconds) Bryan is shy and will not respond to the nurse in any way.
Stage 2: (5 seconds) Bryan has warmed up and says, "Beep," whenever he hears a beep.
Stage 3: (30 seconds) Bryan decides it's more fun to just yell, "BEEP, BEEP, BEEP," whenever he feels like it.
Stage 4: (10 seconds) The nurse changes tactics and asks Bryan to lift up his arms when he hears a beep. Bryan complies.
Stage 5: (30 seconds) The test is boring, but lifting his arms is fun, so Bryan starts flapping his arms franctically and says, "Look, I'm a bird." The nurse gives up.